Polyareneazole/thermoplastic pulp and methods of making same

ABSTRACT

The present invention relates to thermoplastic and polyareneazole pulp for use as reinforcement material in products including for example fluid sealing materials, as a processing aid including its use as a thixotrope, and as a filter material. The pulp comprises (a) irregularly shaped, thermoplastic fiber fibrous structures, (b) irregularly shaped, polyareneazole fibrous structures and (c) water, whereby thermoplastic fiber fibrils and/or stalks are substantially entangled with polyareneazole fibrils and/or stalks. The invention further relates to processes for making such thermoplastic and polyareneazole pulp.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

This invention relates to thermoplastic and polyareneazole pulp for useas a reinforcement material in products including for example fluidsealing materials, as a processing aid including its use as athixotrope, and as a filter material. The invention further relates toprocesses for making such pulp.

2. Description of Related Art.

Fibrous and non fibrous reinforcement materials have been used for manyyears in fluid sealing products and other plastic or rubber products.Such reinforcement materials typically must exhibit high wear and heatresistance.

Asbestos fibers have historically been used as reinforcement materials,but due to their health risks, replacements have been made or proposed.However, many of these replacements do not perform as well as asbestosin one way or another.

Research Disclosure 74-75, published February 1980, discloses themanufacture of pulp made from fibrillated KEVLAR® brand para-aramidfibers of variable lengths and use of such pulp as a reinforcementmaterial in various applications. This publication discloses that pulpmade from KEVLAR® brand para-aramid fibers can be used in sheet productsalone, or in combination with fibers of other materials, such as NOMEX®brand meta-aramid, wood pulp, cotton and other natural cellulosics,rayon, polyester, polyolefin, nylon, polytetrafluoroethylene, asbestosand other minerals, fiberglass and other, ceramics, steel and othermetals, and carbon. The publication also discloses the use of pulp fromKEVLAR® brand para-aramid fiber alone, or with KEVLAR® brand para-aramidshort staple, in friction materials to replace a fraction of theasbestos volume, with the remainder of the asbestos volume beingreplaced by fillers or other fibers.

U.S. Patent Application Publication 2003/0022961 (to Kusaka et al.)discloses friction materials made from a friction modifier, a binder anda fibrous reinforcement made of a mixture of (a) a dry aramid pulp and(b) wet aramid pulp, wood pulp or acrylic fiber pulp. Dry aramid pulp isdefined as an aramid pulp obtained by “the dry fibrillation method”. Thedry fibrillation method is dry milling the aramid fibers between arotary cutter and a screen to prepare the pulp. Wet aramid pulp isdefined as an aramid pulp obtained by “the wet fibrillation method”. Thewet fibrillation method is milling short aramid fibers in water betweentwo rotary discs to form fibrillated fibers and then dehydrating thefibrillated fibers, i.e., the pulp. Kusaka et al further disclose amethod of mix-fibrillating fibers by first mixing plural types oforganic fibers that fibrillate at a definite ratio, and thenfibrillating the mixture to produce a pulp.

Polypyridobisimidazole polymer is a rigid rod polymer. Fiber made fromthis polymer (such as the polymer composition of which is referred to asPIPD and is known as the polymer used to make M5® fiber) is known to beuseful in both cut and flame resistant protective apparel. Rigid-rodpolymer fibers having strong hydrogen bonds between polymer chains,e.g., polypyridobisimidazoles, have been described in U.S. Pat. No.5,674,969 to Sikkema et al. An example of a polypyridobisimidazole ispoly(1,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazole),which can be prepared by the condensation polymerization oftetraaminopyridine and 2,5-dihydroxyterephthalic acid in polyphosphoricacid. Sikkema discloses that pulp can be made from these fibers. Sikkemaalso describes that in making one- or two-dimensional objects, such asfibers, films, tapes, and the like, it is desired thatpolypyridobisimidazoles have a high molecular weight corresponding to arelative viscosity (“Vrel” or “hrel”) of at least about 3.5, preferablyat least about 5, and more particularly equal to or higher than about10, when measured at a polymer concentration of 0.25 g/dl in methanesulfonic acid at 25° C. Sikkema also discloses that good fiber spinningresults are obtained withpoly[pyridobisimidazole-2,6-diyl(2,5-dihydroxy-p-phenylene)] havingrelative viscosities greater than about 12, and that relativeviscosities of over 50 (corresponding to inherent viscosities greaterthan about 15.6 dl/g) can be achieved.

There is an ongoing need to provide alternative pulps that both performwell in products and that are low in cost. Despite the numerousdisclosures proposing lower cost alternative reinforcement materials,many of these proposed products do not adequately perform in use, costsignificantly more than currently commercial products, or have othernegative attributes. As such, there remains a need for reinforcementmaterials that exhibit high wear and heat resistance, and that arecomparable or less expensive than other commercially availablereinforcement materials.

BRIEF SUMMARY OF THE INVENTION

One embodiment of this invention relates to a pulp for use asreinforcement or processing material, comprising:

-   -   (a) irregularly shaped, fibrillated thermoplastic fibrous        structures, the structures being 60 to 97 weight percent of the        total solids;    -   (b) irregularly shaped, fibrillated polyarenazole fibrous        structures being 3 to 40 weight percent of the total solids; and    -   (c) water, the thermoplastic and the polyarenazole fibrous        structures having an average maximum dimension of no more than 5        mm, a length-weighted average length of no more than 1.3 mm, and        stalks and fibrils where the thermoplastic fibrils and/or stalks        are substantially entangled with the polyarenazole fibrils        and/or stalks.

Another embodiment of this invention is a process for making afibrillated thermoplastic and polyarenazole pulp for use asreinforcement material, comprising:

-   -   (a) combining pulp ingredients including:        -   (1) thermoplastic fiber that is capable of being fibrillated            and having an average length of no more than 10 cm and being            60 to 97 weight percent of the total solids in the            ingredients;        -   (2) rigid rod polyarenazole fiber having an average length            of no more than 10 cm and being 3 to 40 weight percent of            the total solids in the ingredients; and        -   (3) water being 95 to 99 weight percent of the total            ingredients;    -   (b) mixing the ingredients to a substantially uniform slurry;    -   (c) co-refining the slurry by simultaneously:        -   (1) fibrillating, cutting and masticating the fibrillated            thermoplastic fiber and the polyarenazole fiber to            irregularly shaped fibrillated fibrous structures with            stalks and fibrils; and        -   (2) dispersing all solids such that the refined slurry is            substantially uniform; and    -   (d) removing water from the refined slurry, thereby producing a        fibrillated thermoplastic and polyarenazole pulp with the        fibrillated thermoplastic and the polyarenazole fibrous        structures having an average maximum dimension of no more than 5        mm, a length-weighted average length of no more than 1.3 mm, and        the fibrillated thermoplastic fibrils and/or stalks are        substantially entangled with the polyarenazole fibrils and/or        stalks.

Still another embodiment of this invention is a process for making anfibrillated thermoplastic and polyarenazole pulp for use asreinforcement and processing material, comprising:

-   -   (a) combining ingredients including water and a first fiber from        the group consisting of:        -   (1) thermoplastic fiber that is capable of being fibrillated            being 60 to 97 weight percent of the total solids in the            pulp; and        -   (2) rigid rod polyarenazole fiber being 3 to 40 weight            percent of the total solids in the pulp;    -   (b) mixing the combined ingredients to a substantially uniform        suspension;    -   (c) refining the suspension in a disc refiner thereby cutting        the fiber to have an average length of no more than 10 cm, and        fibrillating and masticating at least some of the fiber to        irregularly shaped fibrillated fibrous structures;    -   (d) combining ingredients including the refined suspension, the        second fiber of the group of (a)(1 and 2) having an average        length of no more than 10 cm, and water, if necessary, to        increase the water concentration to 95-99 weight percent of the        total ingredients;    -   (e) mixing the ingredients, if necessary, to form a        substantially uniform suspension;    -   (d) co-refining the mixed suspension by simultaneously:        -   (1) fibrillating, cutting and masticating solids in the            suspension such that all or substantially all of the            thermoplastic and polyarenazole fiber is converted to            irregularly shaped fibrillated thermoplastic and            polyarenazole fibrous structures with stalks and fibrils;            and        -   (2) dispersing all solids such that the refined slurry is            substantially uniform; and    -   (f) removing water from the refined slurry, thereby producing an        thermoplastic and polyarenazole pulp with the fibrillated        thermoplastic and the polyarenazole fibrous structures having an        average maximum dimension of no more than 5 mm, a        length-weighted average length of no more than 1.3 mm, and the        thermoplastic fibrils and/or stalks are substantially entangled        with the polyarenazole fibrils and/or stalks.

In some embodiments this invention is further directed to a fluidsealing material, comprising a binder and a fibrous reinforcementmaterial comprising the pulp of the present invention. In otherembodiments this invention is directed to a thixotrope or a filtercomprising the pulp of the present invention.

BRIEF DESCRIPTION OF THE DRAWING(S)

The invention can be more fully understood from the following detaileddescription thereof in connection with accompanying drawings describedas follows.

FIG. 1 is a block diagram of apparatus for performing a wet process formaking “wet” pulp in accordance with the present invention.

FIG. 2 is a block diagram of apparatus for performing a dry process formaking “dry” pulp in accordance with the present invention.

FIG. 3 is a digital optical micrograph of the prior art material that ismade when thermoplastic fiber is refined without any polyareneazole(PBO) fiber being present.

FIG. 4 is a digital optical micrograph of the fibrillation of PBO fiberafter refining.

FIG. 5 is a digital optical micrograph of the fibrillation of oneembodiment of PBO and polypropylene fiber after co-refining.

FIG. 6 is a digital optical micrograph of the fibrillation of anotherembodiment of PBO and polypropylene fiber after co-refining.

FIG. 7 is a digital optical micrograph of the fibrillation of yetanother embodiment of PBO and polypropylene fiber after co-refining.

GLOSSARY

Before the invention is described, it is useful to define certain termsin the following glossary that will have the same meaning throughoutthis disclosure unless otherwise indicated.

“Fiber” means a relatively flexible, unit of matter having a high ratioof length to width across its cross-sectional area perpendicular to itslength. Herein, the term “fiber” is used interchangeably with the term“filament” or “end”. The cross section of the filaments described hereincan be any shape, but are typically circular or bean shaped. Fiber spunonto a bobbin in a package is referred to as continuous fiber orcontinuous filament or continuous filament yarns. Fiber can be cut intoshort lengths called staple fiber. Fiber can be cut into even smallerlengths called floc. Yarns, multifilament yarns or tows comprise aplurality of fibers. Yarn can be intertwined and/or twisted.

“Fibril” means a small fiber having a diameter as small as a fraction ofa micrometer to a few micrometers and having a length of from about 10to 100 micrometers. Fibrils generally extend from the main trunk of alarger fiber having a diameter of from 4 to 50 micrometers. Fibrils actas hooks or fasteners to ensnare and capture adjacent material. Somefibers fibrillate, but others do not or do not effectively fibrillateand for purposes of this definition such fibers do not fibrillate.

“Fibrillated fibrous structures” means particles of material having astalk and fibrils extending therefrom wherein the stalk is generallycolumnar and about 10 to 50 microns in diameter and the fibrils arehair-like members only a fraction of a micron or a few microns indiameter attached to the stalk and about 10 to 100 microns long.

“Floc” means short lengths of fiber, shorter than staple fiber. Thelength of floc is about 0.5 to about 15 mm and a diameter of 4 to 50micrometers, preferably having a length of 1 to 12 mm and a diameter of8 to 40 micrometers. Floc that is less than about 1 mm does not addsignificantly to the strength of the material in which it is used. Flocor fiber that is more than about 15 mm often does not function wellbecause the individual fibers may become entangled and cannot beadequately and uniformly distributed throughout the material or slurry.Aramid floc is made by cutting aramid fibers into short lengths withoutsignificant or any fibrillation, such as those prepared by processesdescribed in U.S. Pat. Nos. 3,063,966, 3,133,138, 3,767,756, and3,869,430.

“Arithmetric” length means the calculated length from the followingformula:${{Arithmetric}\quad{length}} = \frac{\sum\left\lbrack \left( {{Each}\quad{Individual}\quad{pulp}\quad{length}} \right) \right\rbrack}{\sum\left\lbrack {{Individual}\quad{pulp}\quad{count}} \right\rbrack}$

“Length-weighted average” length means the calculated length from thefollowing formula:${{Length}\text{-}{weighted}\quad{average}\quad{length}} = \frac{\sum\left\lbrack \left( {{Each}\quad{Individual}\quad{pulp}\quad{length}} \right)^{2} \right\rbrack}{\sum\left\lbrack {{Each}\quad{Individual}\quad{pulp}\quad{length}} \right\rbrack}$

“Weight-weighted average” length means the calculated length from thefollowing formula:${{Weight}\text{-}{weighted}\quad{average}\quad{length}} = \frac{\sum\left\lbrack \left( {{Each}\quad{Individual}\quad{pulp}\quad{length}} \right)^{3} \right\rbrack}{\sum\left\lbrack \left( {{Each}\quad{Individual}\quad{pulp}\quad{length}} \right)^{2} \right\rbrack}$

“Maximum dimension” of an object means the straight distance between thetwo most distal points from one another in the object

“Staple fiber” can be made by cutting filaments into lengths of no morethan 15 cm, preferably 3 to 15 cm; and most preferably 3 to 8 cm. Thestaple fiber can be straight (i.e., non crimped) or crimped to have asaw tooth shaped crimp along its length, with any crimp (or repeatingbend) frequency. The fibers can be present in uncoated, or coated, orotherwise pretreated (for example, pre-stretched or heat-treated) form.

DETAILED DESCRIPTION OF THE INVENTION

This invention is directed to polyareneazole and thermoplastic fiberpulp that has use as reinforcement material, fluid sealing materials,processing aids, and filters, and other materials that incorporate thispulp. The invention is also directed to processes for making apolyareneazole and thermoplastic fiber pulp

I. FIRST EMBODIMENT OF THE INVENTIVE PROCESS

In a first embodiment, the process for making an thermoplastic fiber andpolyareneazole pulp comprises the following steps. First, pulpingredients are combined, added or contacted together. Second, thecombined pulp ingredients are mixed to a substantially uniform slurry.Third, the slurry is simultaneously refined or co-refined. Fourth, wateris removed from the refined slurry.

Combining Step

In the combining step, the pulp ingredients are preferably addedtogether in a container. In a preferred embodiment the pulp ingredientsinclude (1) thermoplastic fiber, (2) polyareneazole fiber, (3)optionally other additives, and (4) water.

Thermoplastic Fiber

The thermoplastic fiber is added to a concentration of 60 to 97 wt % ofthe total solids in the ingredients and preferably 60 to 75 wt % of thetotal solids in the ingredients.

The thermoplastic fiber preferably has an average length of no more than10 cm, more preferably 0.5 to 5 cm, and most preferably 0.6 to 2 cm. Thethermoplastic fiber also has a linear density of no more than 10 dtex.Prior to combining the pulp ingredients together, any thermoplasticfibers in the form of continuous filaments can be cut into shorterfibers, such as staple fibers or floc.

Thermoplastic Fiber Polymer

By thermoplastic fiber it is meant that these fibers are made fromthermoplastic polymers. Thermoplastic polymers when heated, flow in themanner of a highly viscous liquid; they can be solidified by cooling andupon reheating they return to a liquid state. Polymers suitable for usein making the thermoplastic fiber must be of fiber-forming molecularweight in order to be shaped into fibers. The polymers can includehomopolymers, copolymers, and mixtures thereof. Typical thermoplasticpolymers can be made to flow and solidified reversibly time and timeagain by subsequent heating and cooling. In the heated viscous liquidstate thermoplastic polymers can be formed into fibers and other shapedstructures. The liquid polymer is then typically cooled to solidify thefibers and shaped structures.

In a most preferred embodiment, the thermoplastic fiber useful in thisinvention includes thermoplastic polymers based on polyolefins andpolyesters. Representative polyolefins include polypropylenes,polyethylenes, and mixtures thereof, and in addition higher chainpolyolefins can also be used. Representative polyesters includepolyethylene terephthalates, polyethylene napthalates and mixturesthereof, and in addition others in the polyester family can be used.

Other thermoplastic fibers useful in this invention include, but are notlimited to, fibers from thermotropic liquid crystalline polymers, fibersfrom aliphatic polyamides, fibers from fluoropolymers, and fibers frompolyvinyl alcohol.

Polvareneazole Fiber

The polyareneazole fiber is added to a concentration of 3 to 40 wt % ofthe total solids in the ingredients, and preferably 25 to 40 wt % of thetotal solids in the ingredients. The polyareneazole fiber preferably hasa linear density of no more than 10 dtex and more preferably 0.8 to 2.5dtex. The polyareneazole fiber also preferably has an average lengthalong its longitudinal axis of no more than 10 cm, more preferably anaverage length of 0.65 to 2.5 cm, and most preferably an average lengthof 0.65 to 1.25 cm.

Polvarenazole Polymer

Polymers suitable for use in making the polyarenazole fiber must be offiber-forming molecular weight in order to be shaped into fibers. Thepolymers can include homopolymers, copolymers, and mixtures thereof

As defined herein, “polyareneazole” refers to polymers having either:

-   one heteroaromatic ring fused with an adjacent aromatic group (Ar)    of repeating unit structure (a):    with N being a nitrogen atom and Z being a sulfur, oxygen, or NR    group with R being hydrogen or a substituted or unsubstituted alkyl    or aryl attached to N; or two hetero aromatic rings each fused to a    common aromatic group (Ar¹) of either of the repeating unit    structures (b1 or b2):    wherein N is a nitrogen atom and B is an oxygen, sulfur, or NR    group, wherein R is hydrogen or a substituted or unsubstituted alkyl    or aryl attached to N. The number of repeating unit structures    represented by structures (a), (b1), and (b2) is not critical. Each    polymer chain typically has from about 10 to about 25,000 repeating    units. Polyareneazole polymers include polybenzazole polymers and/or    polypyridazole polymers. In certain embodiments, the polybenzazole    polymers comprise polybenzimidazole or polybenzobisimidazole    polymers. In certain other embodiments, the polypyridazole polymers    comprise polypyridobisimidazole or polypyridoimidazole polymers. In    certain preferred embodiments, the polymers are of a    polybenzobisimidazole or polypyridobisimidazole type.

In structure (b1) and (b2), Y is an aromatic, heteroaromatic, aliphaticgroup, or nil; preferably an aromatic group; more preferably asix-membered aromatic group of carbon atoms. Still more preferably, thesix-membered aromatic group of carbon atoms (Y) has para-orientedlinkages with two substituted hydroxyl groups; even more preferably2,5-dihydroxy-para-phenylene.

In structures (a), (b1), or (b2), Ar and Ar¹ each represent any aromaticor heteroaromatic group. The aromatic or heteroaromatic group can be afused or non-fused polycyclic system, but is preferably a singlesix-membered ring. More preferably, the Ar or Ar¹ group is preferablyheteroaromatic, wherein a nitrogen atom is substituted for one of thecarbon atoms of the ring system or Ar or Ar¹ may contain only carbonring atoms. Still more preferably, the Ar or Ar¹ group isheteroaromatic.

As herein defined, “polybenzazole” refers to polyareneazole polymerhaving repeating structure (a), (b1), or (b2) wherein the Ar or Ar¹group is a single six-membered aromatic ring of carbon atoms.Preferably, polybenzazoles include a class of rigid rod polybenzazoleshaving the structure (b1) or (b2); more preferably rigid rodpolybenzazoles having the structure (b1) or (b2) with a six-memberedcarbocyclic aromatic ring Ar¹ . Such preferred polybenzazoles include,but are not limited to polybenzimidazoles (B═NR), polybenzthiazoles(B═S), polybenzoxazoles (B═O), and mixtures or copolymers thereof. Whenthe polybenzazole is a polybenzimidazole, preferably it ispoly(benzo[1,2-d:4,5-d′]bisimidazole-2,6-diyl-1,4-phenylene). When thepolybenzazole is a polybenzthiazole, preferably it ispoly(benzo[1,2-d:4,5-d′]bisthiazole-2,6-diyl-1,4-phenylene). When thepolybenzazole is a polybenzoxazole, preferably it is poly(benzo[1,2-d:4,5-d′]bisoxazole-2,6-d iyl-1,4-phenylene).

As herein defined, “polypyridazole” refers to polyareneazole polymerhaving repeating structure (a), (b1), or (b2) wherein the Ar or Ar¹group is a single six-membered aromatic ring of five carbon atoms andone nitrogen atom. Preferably, these polypyridazoles include a class ofrigid rod polypyridazoles having the structure (b1) or (b2), morepreferably rigid rod polypyridazoles having the structure (b1) or (b2)with a six-membered heterocyclic aromatic ring Ar¹ . Such more preferredpolypyridazoles include, but are not limited to polypyridobisimidazole(B═NR), polypyridobisthiazole (B═S), polypyridobisoxazole (B═O), andmixtures or copolymers thereof. Yet more preferred, the polypyridazoleis a polypyridobisimidazole (B═NR) of structure:

wherein N is a nitrogen atom and R is hydrogen or a substituted orunsubstituted alkyl or aryl attached to N, preferably wherein R is H.The average number of repeat units of the polymer chains is typically inthe range of from about from about 10 to about 25,000, more typically inthe range of from about 100 to 1,000, even more typically in the rangeof from about 125 to 500, and further typically in the range of fromabout 150 to 300.

For the purposes of this invention, the relative molecular weights ofthe polyareneazole polymers are suitably characterized by diluting thepolymer products with a suitable solvent, such as methane sulfonic acid,to a polymer concentration of 0.05 g/dl, and measuring one or moredilute solution viscosity values at 30° C. Molecular weight developmentof polyareneazole polymers of the present invention is suitablymonitored by, and correlated to, one or more dilute solution viscositymeasurements. Accordingly, dilute solution measurements of the relativeviscosity (“Vrel” or “hrel” or “nrel”) and inherent viscosity (“Vinh” or“hinh” or “ninh”) are typically used for monitoring polymer molecularweight. The relative and inherent viscosities of dilute polymersolutions are related according to the expressionVinh=In (Vrel)/C,where In is the natural logarithm function and C is the concentration ofthe polymer solution. Vrel is a unitless ratio of the polymer solutionviscosity to that of the solvent free of polymer, thus Vinh is expressedin units of inverse concentration, typically as deciliters per gram(“dl/g”). Accordingly, in certain aspects of the present invention thepolypyridoimidazole polymers are produced that are characterized asproviding a polymer solution having an inherent viscosity of at leastabout 20 dl/g at 30° C. at a polymer concentration of 0.05 g/dl inmethane sulfonic acid. Because the higher molecular weight polymers thatresult from the invention disclosed herein give rise to viscous polymersolutions, a concentration of about 0.05 g/dl polymer in methanesulfonic acid is useful for measuring inherent viscosities in areasonable amount of time.

In some embodiments, this invention utilizes polyareneazole fiber thathas an inherent viscosity of at least 20 dl/g; in other more preferredembodiments the inherent viscosity is of at least 25 dl/g; and in somemost preferred embodiments the inherent viscosity is of at least 28dl/g.

Optional Other Additives

Other additives can optionally be added as long as they stay suspendedin the slurry in the mixing step and do not significantly change theeffect of the refining step on the mandatory solid ingredients listedabove. Suitable additives include pigments, dyes, anti-oxidants,flame-retardant compounds, and other processing and dispersing aids.Preferably, the pulp ingredients do not include asbestos. In otherwords, the resulting pulp is asbestos free or without asbestos.

Water

Water is added to a concentration of 95 to 99 wt % of the totalingredients, and preferably 97 to 99 wt % of the total ingredients.Further, the water can be added first. Then other ingredients can beadded at a rate to optimize dispersion in the water while simultaneouslymixing the combined ingredients.

Mixing Step

In the mixing step, the ingredients are mixed to a substantially uniformslurry. By “substantially uniform” is meant that random samples of theslurry contain the same wt % of the concentration of each of thestarting ingredients as in the total ingredients in the combination stepplus or minus 10 wt %, preferably 5 wt % and most preferably 2 wt %. Forinstance, if the concentration of the solids in the total mixture is 50wt % thermoplastic fiber plus 50 wt % polyareneazole fiber, then asubstantially uniform mixture in the mixing step means each randomsample of the slurry has (1) a concentration of the thermoplastic fiberof 50 wt % plus or minus 10 wt %, preferably 5 wt % and most preferably2 wt % and (2) a concentration of polyareneazole fiber of 50 wt % plusor minus 10 wt %, preferably 5 wt % and most preferably 2 wt %. Themixing can be accomplished in any vessel containing rotating blades orsome other agitator. The mixing can occur after the ingredients areadded or while the ingredients are being added or combined.

Refining Step

In the refining step the pulp ingredients are simultaneously co-refined,converted or modified as follows. The thermoplastic fiber and thepolyareneazole fiber are fibrillated, cut and masticated to irregularlyshaped fibrous structures having stalks and fibrils. All solids aredispersed such that the refined slurry is substantially uniform.“Substantially uniform” is as defined above. The refining steppreferably comprises passing the mixed slurry through one or more discrefiner, or recycling the slurry back through a single refiner. By theterm “disc refiner” is meant a refiner containing one or more pair ofdiscs that rotate with respect to each other thereby refiningingredients by the shear action between the discs. In one suitable typeof disc refiner, the slurry being refined is pumped between closelyspaced circular rotor and stator discs rotatable with respect to oneanother. Each disc has a surface, facing the other disc, with at leastpartially radially extending surface grooves. A preferred disc refinerthat can be used is disclosed in U.S. Pat. No. 4,472,241. In a preferredembodiment, the plate gap setting for the disc refiner is a maximum of0.18 mm and preferably the gap setting is 0.13 mm or lower, to apractical minimum setting of about 0.05 mm.

If necessary for uniform dispersion and adequate refining, the mixedslurry can be passed through the disc refiner more than once or througha series of at least two disc refiners. When the mixed slurry is refinedin only one refiner, there is a tendency for the resulting slurry to beinadequately refined and non uniformly dispersed. Conglomerates oraggregates entirely or substantially of one solid ingredient, or theother, or both, can form rather than being dispersed forming asubstantially uniform dispersion. Such conglomerates or aggregates havea greater tendency to be broken apart and dispersed in the slurry whenthe mixed slurry is passed through the refiner more than once or passedthrough more than one refiner. Optionally, the refined slurry may bepassed through a screen to segregate long fibers or clumps, which may berecycled through one or more refiners until cut to acceptable lengths orconcentration.

Because a substantially uniform slurry containing multiple ingredientsis co-refined in this step of the process, any one type of pulpingredient (for example, polyareneazole fiber) is refined into a pulp inthe presence of all the other types of pulp ingredients (for example,thermoplastic fiber) while those other ingredients are also beingrefined. This co-refining of pulp ingredients forms a pulp that issuperior to a pulp blend generated by merely mixing two pulps together.Adding two pulps and then merely mixing them together does not form thesubstantially uniform and intimately connected fibrous components of thepulp generated by co-refining of pulp ingredients into pulp inaccordance with the present invention.

Removing Step

After the refining step, the water is removed from the refined slurry.The water can be removed by collecting the pulp on a dewatering devicesuch as a horizontal filter, and if desired, additional water can beremoved by applying pressure or squeezing the pulp filter cake. Thedewatered pulp can optionally then be dried to a desired moisturecontent, and/or can be packaged or wound up on rolls. In some preferredembodiments, the water is removed to a degree that the resulting pulpcan be collected on a screen and wound up into rolls. In someembodiments, no more than about 60 total wt % water being present is adesired amount of water and preferably 4 to 60 total wt % water.However, in some embodiments, the pulp can retain more water, so higheramounts of total water, as much as 75 total wt % water, will be present.

FIGS. 1 and 2

This process will now be described in reference to FIGS. 1 and 2.Throughout this detailed description, similar reference characters referto similar elements in all figures of the drawings.

Referring to FIG. 1, there is a block diagram of an embodiment of a wetprocess for making “wet” pulp in accordance with the present invention.Pulp ingredients 1 are added to container 2. Container 2 is providedwith an internal mixer, similar to a mixer in a washing machine. Themixer disperses the ingredients into the water creating thesubstantially uniform slurry. The mixed slurry is transferred to a firstrefiner 3 that refines the slurry. Then, optionally, the refined slurrycan be transferred to a second refiner 4, and optionally then to a thirdrefiner 5. Three refiners are illustrated but any number of refiners canbe used depending on the degree of uniformity and refining desired.After the last refiner in the series of refiners, the refined slurry isoptionally transferred to a filter or sorter 6 that allows slurry withdispersed solids below a chosen mesh or screen size to pass andrecirculates dispersed solids larger than a chosen mesh or screen sizeback to one or more of the refiners such as through line 7 or to arefiner 8 dedicated to refine this recirculated slurry from whichrefined slurry is again passed to the filter or sorter 6. Suitablyrefined slurry passes from the filter or sorter 6 to a horizontal watervacuum filter 9 that removes water. Slurry can be transferred from pointto point by any conventional method and apparatus such as with theassistance of one or more pump 10. Then the pulp is conveyed to a dryer11 that removes more water until the pulp has the desired concentrationof water. Then the refined pulp is packaged in a baler 12.

Referring to FIG. 2, there is a block diagram of an embodiment of a dryprocess for making “dry” pulp in accordance with the present invention.This dry process is the same as the wet process except after thehorizontal water vacuum filter 9. After that filter, the pulp goesthrough a press 13 that removes more water until the pulp has thedesired concentration of water. Then the pulp goes through a fluffer 14to fluff the pulp and then a dryer 11 to remove more water. Then, thepulp is passed through a rotor 15 and packaged in a baler 12.

II. SECOND EMBODIMENT OF THE INVENTION PROCESS

In a second embodiment, the process for making the thermoplastic andpolyareneazole pulp is the same as the first embodiment of the processdescribed above with the following differences.

Prior to combining all ingredients together, either the thermoplasticfiber or the polyareneazole fiber, or both the thermoplastic fiber andthe polyareneazole fiber, may need to be shortened. This is done bycombining water with the fiber ingredient. Then the water and fiber aremixed to form a first suspension and processed through a first discrefiner to shorten the fiber. The disc refiner cuts the fiber to anaverage length of no more than 10 cm. The disc refiner will alsopartially fibrillate and partially masticate the fiber. The other fiber,that was not previously added, can be shortened this way too forming asecond processed suspension. Then the other fiber (or the secondsuspension, if processed in water) is combined with the firstsuspension.

More water is added before or after, or when, other ingredients areadded, if necessary, to increase the water concentration to 95-99 wt %of the total ingredients. After all ingredients are combined, they canbe mixed, if necessary, to achieve a substantially uniform slurry.

The ingredients in the slurry are then co-refined together, i.e.,simultaneously. This refining step includes fibrillating, cutting andmasticating solids in the suspension such that all or substantially allof the thermoplastic fiber and polyareneazole fiber is converted toirregularly shaped fibrillated fibrous structures. This refining stepalso disperses all solids such that the refined slurry is substantiallyuniform. Then water is removed as in the first embodiment of theprocess. Both processes produce the same or substantially the samethermoplastic fiber and polyareneazole pulp.

The Inventive Pulp

The resulting product produced by the process of this invention is athermoplastic fiber and polyareneazole pulp for use as reinforcementmaterial in products. The pulp comprises (a) irregularly shaped,thermoplastic fiber fibrous structures, (b) irregularly shaped,polyareneazole fibrous structures, (c) optionally other minor additives,and (d) water.

The concentration of the separate ingredient components in the pulpcorrespond, of course, to the concentrations described beforehand of thecorresponding ingredients used in making the pulp.

The irregularly shaped, thermoplastic fiber and polyareneazolefibrillated fibrous structures have stalks and fibrils. Thethermoplastic fiber fibrils and/or stalks are substantially entangledwith the polyareneazole fibrils and/or stalks. The fibrils are importantand act as hooks or fasteners or tentacles that adhere to and holdadjacent particles in the pulp and final product thereby providingintegrity to the final product.

The thermoplastic fiber and polyareneazole fibrillated fibrousstructures preferably have an average maximum dimension of no more than5 mm, more preferably 0.1 to 4 mm, and most preferably 0.1 to 3 mm. Thethermoplastic fiber and polyareneazole fibrillated fibrous structurespreferably have a length-weighted average of no more than 1.3 mm, morepreferably 0.7 to 1.2 mm, and most preferably 0.75 to 1.1 mm.

The thermoplastic fiber and polyareneazole pulp are without substantialaggregates or conglomerates of the same material. Further, the pulp hasa Canadian Standard Freeness (CSF) as measured per TAPPI test T 227om-92, which is a measure of its drainage characteristics, of 100 to 700ml, and preferably 250 to 450 ml.

Surface area of pulp is a measure of the degree of fibrillation andinfluences the porosity of the product made from the pulp. In someembodiments of this invention the surface area of pulp is 7 to 11 squaremeters per gram.

It is believed that the fibrillated fibrous structures, dispersedsubstantially homogeneously throughout the reinforcement material andthe fluid sealing materials, provide, by virtue of the high temperaturecharacteristics of the polyareneazole polymers and the fibrillationpropensity of the polyareneazole fibers, many sites of reinforcement.Therefore, when co-refined, the thermoplastic and polyareneazolematerials are in such intimate contact that in a fluid sealing materialthere are always some polyareneazole fibrous structures close to thethermoplastic fiber structures so the stresses and abrasion of serviceare always shared

Fluid Sealing Material

The invention is further directed to fluid sealing material andprocesses for making the fluid sealing materials. Fluid sealingmaterials are used in or as a barrier to prevent the discharge of fluidsand/or gases and used to prevent the entrance of contaminants where twoitems are joined together. An illustrative use for fluid sealingmaterial is in gaskets. The fluid sealing material comprises a binder;optionally at least one filler; and a fibrous reinforcement materialcomprising the thermoplastic and polyareneazole pulp of this invention.Suitable binders include nitrile rubber, butadiene rubber, neoprene,styrene-butadiene rubber, nitrile-butadiene rubber, and mixturesthereof. The binder can be added with all other starting materials. Thebinder is typically added in the first step of the gasket productionprocess, in which the dry ingredients are mixed together. Otheringredients optionally include uncured rubber particles and a rubbersolvent, or a solution of rubber in solvent, to cause the binder to coatsurfaces of the fillers and pulp. Suitable fillers include bariumsulfate, clays, talc, and mixtures thereof.

Suitable processes for making fluid sealing materials are, for example,a beater-add process or wet process where the gasket is made from aslurry of materials, or by what is called a calendering or dry processwhere the ingredients are combined in an elastomeric or rubber solution.

Many other applications of the pulp are possible, including its use as aprocessing aid such as a thixotrope, its use as reinforcement ofconcrete or masonry material, or its us as a filter material. When usedas a filter material typically the pulp of this invention is combinedwith a binder and a sheet or paper product is made by conventionalmethods.

Test Methods

The following test methods were used in the following Examples.

Canadian Standard Freeness (CSF) was measured as described in TAPPImethod T 227 in conjunction with optical microscopy. CSF measures thedrainage rate of a dilute pulp suspension. It is a useful test to assessthe degree of fibrillation. Data obtained from conduct of that test areexpressed as Canadian Freeness Numbers, which represent the millilitersof water that drain from an aqueous slurry under specified conditions. Alarge number indicates a high freeness and a high tendency for water todrain. A low number indicates a tendency for the dispersion to drainslowly. The freeness is inversely related to the degree of fibrillationof the pulp, since greater numbers of fibrils reduce the rate at whichwater drains through a forming paper mat.

Average fiber lengths, including Length-weighted average length, weredetermined using a Fiber Quality Analyzer (sold by OpTest EquipmentInc., 900 Tupper St., Hawkesbury, ON, K6A 3S3 Canada) following TAPPItest method T 271.

Temperature: All temperatures are measured in degrees Celsius (° C.).

Denier is measured according to ASTM D 1577 and is the linear density ofa fiber as expressed as weight in grams of 9000 meters of fiber.

The denier is measured on a Vibroscope from Textechno of Munich,Germany. Denier times (10/9) is equal to decitex (dtex).

EXAMPLES

This invention will now be illustrated by the following specificexamples. All parts and percentages are by weight unless otherwiseindicated. Examples prepared according to the process or processes ofthe current invention are indicated by numerical values. Comparativeexamples prepared are indicated by letters.

The following examples illustrate the surprising increase in the degreeof fibrillation of a thermoplastic fiber by co-refining a small amountof polyarenazole fiber in the presence of the thermoplastic fiber. Thedegree of fibrillation is an important characteristic of a pulp product.There is a direct relationship between degree of fibrillation and fillerretention. In addition, fibrillation is useful to achieve uniformdispersion of the pulp products in a variety of materials. A highlyfibrillated fiber will also be able to bond to a matrix more intenselythrough physical entanglement than a non-fibrillated fiber. In theexamples that follow, poly(paraphenylene benzobisoxazole) (PBO) fiberwas used as a representative of the polyarenazole fiber family andpolypropylene (PP) fiber was used to represent thermoplastic fibers.

Comparative Example A

This example illustrates prior art material that is made whenthermoplastic fiber is refined without any polyarenazole fiber beingpresent.

68.1 grams of a 3.3 dtex polypropylene (PP) fiber cut to 6.4 mm (sold byMiniFIBERS, Inc., 2923 Boones Creek Road, Johnson City, Tenn. 37615) wasdispersed in 2.7 L of water. The dispersion was passed 17 times througha Sprout-Wadron single-speed, 30 cm single disk refiner (sold byAndritz, Inc., Sprout-Bauer Equipment, Muncy, Pa. 17756) with the diskgap set to 0.13 mm. The properties of the as-produced 100% refined PPare shown in Table 1; FIG. 3 is a digital optical micrograph of thematerial showing the limited fibrillation experienced by this materialafter refining.

A paper was then made from the refined material by dispersing with alaboratory pulp disintegrator 6.7 grams of the material (on a dry weightbasis) in 1.5 L water for 3 min, adding the dispersion to a wet-laidpaper mold having a screen with the dimensions of 21 cm×21 cm. Thedispersion was then diluted with 5 L of water and a wet-laid paper wasformed on the screen and excess water was removed with a rolling pin.The paper was then dried at 100° C. for 10 min in a paper dryer. The100% refined thermoplastic material made in this example did not possesappreciable fibrillated fibers and did not produce a stable hand sheet.

Comparative Example B

This example illustrates a 100% polyarenazole pulp. A 100% PBO pulp wasproduced using the same procedure as in Example A with the exception ofusing 68.1 grams of a 1.7 dtex PBO fiber having a cut length of 12.7 mm(sold by Toyobo Co., Ltd., Zylon Department, 2-2-8 Dojima-Hama, Kita-KuOsaka) rather than the polypropylene fiber. The properties of theas-produced 100% PBO refined material are shown in Table 1; FIG. 4 is adigital optical micrograph of the pulp showing the fibrillation of thePBO fiber after refining. A paper was then made (as described inComparative Example A) from the PBO refined material and properties ofthe as-produced paper are shown in Table 2.

Example 1

A pulp of this invention was produced using the same procedure as inExample A with the exception a dispersion containing a mixture of thestarting unrefined cut fibers of Example A and the starting unrefinedcut fibers of Example B was refined, passing 17 times through the diskrefiner to form a co-refined pulp. The fiber mixture contained 61.7grams of a 3.3 dtex fiber polypropylene fiber(PP) cut to 6.4 mm (sold byMiniFIBERS, Inc., 2923 Boones Creek Road, Johnson City, Tenn. 37615 and6.4 grams of 1.7 dtex PBO fiber having a cut length of 12.7 mm (sold byToyobo Co., Ltd., Zylon Department, 2-2-8 Dojima-Hama, Kita-Ku Osaka).Properties of the as-produced pulp are shown in Table 1. A paper wasthen made from the pulp as in Example A and properties of theas-produced paper are shown in Table 1. FIG. 5 is a digital opticalmicrograph of the pulp showing the fibrillation of both the PBO and PPfiber after refining. A paper was then made (as described in ComparativeExample A) from the pulp and properties of the as-produced paper areshown in Table 2.

Example 2

Another pulp of this invention was produced using the same procedure asin Example 1 with the exception the mixture contained 50.8 grams of the3.3 dtex fiber polypropylene fiber (PP) and 17.3 grams of the 1.7 dtexPBO fiber. The co-refined pulp had approximately 25 weight percent PBOand 75 weight percent PP. The properties of the as-produced pulp areshown in Table 1; FIG. 6 is a digital optical micrograph of the pulpshowing the fibrillation of both the PBO and PP fiber after refining. Apaper was then made (as described in Comparative Example A) from thepulp and properties of the as-produced paper are shown in Table 2.

Example 3

Another pulp of this invention was produced using the same procedure asin Example 1 with the exception the mixture contained 40.9 grams of the3.3 dtex fiber polypropylene fiber and 27.2 grams of the 1.7 dtex PBOfiber. The co-refined pulp had approximately 25 weight percent PBO and75 weight percent PP. The properties of the as-produced pulp are shownin Table 1; FIG. 7 is a digital optical micrograph of the pulp showingthe fibrillation of both the PBO and PP fiber after refining. A paperwas then made from the pulp as in Example 1 and properties of theas-produced paper are shown in Table 2.

Example 4

The paper hand sheets of Examples 2 and 3 were each compressed for 2 minat 180° C. and 1.8 MPa and 200° C. and 3.5 MPA. The properties of the asproduced heat-bonded hand sheets are listed in Table 3.

Comparative Example C

The example demonstrates that refining the thermoplastic fibersseparately from the polyareneazole fibers and then mixing them togetherresults in a pulp that provides a paper having lower tensile strength(and therefore less fibrillation) than a paper made from the co-refinedpulp of this invention.

A sample of the refined material made in Comparative Example A was mixedwith a sample of the refined material of Comparative Example B in anamount of 75 wt % polypropylene material to 25% wt % PBO material (dryweight basis) using a standard pulp disintegrator as described inAppendix A of TAPPI 205 for 5 min. The TAPPI disintegrator was used tomix the two refined pulps of Comparative Examples A and B because theagitation is vigorous enough to mix and disperse the previously refinedpulps well, but it would not change their length or fibrillation. Theproperties of the as-produced pulp are shown in Table 1. A paper wasthen made (as described in Comparative Example A) from the pulp andproperties of the as-produced paper are shown in Table 2. Comparing thestrength of the paper from Example 2 with the paper made from thisexample reveals the paper made from the co-refined pulp hadsignificantly improved physical properties (for example a tensilestrength of 0.12 N/cm for the paper from the co-refined pulp versus 0.07N/cm for the paper made from the pulp of this example.)

With the addition of the polyarenazole fiber to the thermoplastic fiber,and then refining the two fibers together as in Examples 1, 2, and 3,the resulting thermoplastic fibers display a higher degree offibrillation and hand sheets could be made. TABLE 1 Length WeightArithm. weighted weighted Pulp mean mean mean from wt % Wt % lengthlength length example PP PBO [mm] [mm] [mm] A 100 0 0.269 0.592 1.317 B0 100 0.169 0.667 2.066 1 91 9 0.140 0.410 2.053 2 75 25 0.138 0.3321.295 3 60 40 0.157 0.568 2.374 Comparative 75 25 0.173 0.678 1.962Example C

TABLE 2 Pulp Surface Tensile Young's Basis from wt % Wt % Area StrengthModulus Density Weight example PP PBO [m²/g] [N/cm] [MPa] [g/cc] [g/m²]A 100 0 1.0 N/A N/A N/A N/A B 0 100 22.1 0.54 4.00 0.35 161.5 1 91 9 2.30.09 0.55 0.25 156.1 2 75 25 4.6 0.12 0.48 0.29 163.5 3 60 40 7.4 0.240.96 0.33 166.9 Comparative 75 25 N/A 0.07 0.21 0.18 161.3 Example C

TABLE 3 Pulp Tensile Young's Basis from wt % Wt % Temp Press StrengthModulus Density Weight example PP PBO [° C.] [MPa] [N/cm] [MPa] [g/cc][g/m²] 2 75 25 180 1.8 16.04 762.0 0.60 148.2 3 60 40 180 1.8 37.02570.6 0.64 155.0 2 75 25 200 3.5 49.08 1653.5 0.80 147.2 3 60 40 200 3.564.09 1150.6 0.80 159.1

Example 5

This example illustrates how the pulp of this invention can beincorporated into a beater-add gasket for fluid sealing applications.Water, rubber, latex, fillers, chemicals, and the pulp of this inventionare combined in desired amounts to form a slurry. On a circulating wiresieve (such as a paper machine screen or wire), the slurry is largelydrained of its water content, is dried in a heating tunnel, and isvulcanized on heated calender rolls to form a material having a maximumthickness of around 2.0 mm. This material is compressed in a hydraulicpress or two-roll calender, which increases the density and improvessealability.

Such beater-add gasket materials generally do not have as goodsealability as equivalent compressed-fiber materials and are best suitedfor moderate-pressure high-temperature applications. Beater-add gasketsfind applicability in the making of auxiliary engine gaskets or, afterfurther processing, cylinder head gaskets. For this purpose, thesemi-finished product is laminated onto both sides of a spiked metalsheet and is physically fixed in place by the spikes.

Example 6

This example illustrates how the pulp of this invention can beincorporated into a gasket made by a calendering process. The sameingredients as in Example 5, minus the water, are thoroughly dry mixedtogether and are then blended with a rubber solution prepared using anappropriate solvent.

After mixing, the compound is then generally conveyed batchwise to aroll calender. The calender consists of a small roll that is cooled anda large roll that is heated. The compound is fed and drawn into thecalender nip by the rotary movement of the two rolls. The compound willadhere and wrap itself around the hot lower roll in layers generallyabout 0.02 mm thick, depending on the pressure, to form a gasketingmaterial made from the built-up compound layers. In so doing, thesolvent evaporates and vulcanization of the elastomer commences.

Once the desired gasketing material thickness is reached, the rolls arestopped and the gasketing material is cut from the hot roll and cutand/or punched to the desired size. No additional pressing or heating isrequired, and the material is ready to perform as a gasket. In thismanner gaskets up to about 7 mm thick can be manufactured. However, mostgaskets made in this manner are much thinner, normally being about 3 mmor less in thickness.

1. A pulp for use as reinforcement or processing material, comprising:(a) fibrillated thermoplastic fibrous structures, the structures being60 to 97 weight percent of the total solids; (b) fibrillatedpolyarenazole fibrous structures being 3 to 40 weight percent of thetotal solids; the thermoplastic and the polyarenazole fibrous structureshaving an average maximum dimension of no more than 5 mm, alength-weighted average length of no more than 1.3 mm, and stalks andfibrils where the thermoplastic fibrils and/or stalks are substantiallyentangled with the polyarenazole fibrils and/or stalks.
 2. The pulp ofclaim 1, wherein the thermoplastic fibrous structures are about 60 to 75weight percent of the total solids.
 3. The pulp of claim 1, wherein thepolyarenazole fibrous structures are about 25 to 40 weight percent ofthe total solids.
 4. The pulp of claim 1 having a Canadian StandardFreeness (CSF) of 100 to 700 ml.
 5. The pulp of claim 1, wherein thethermoplastic fibrous structures are polyolefin structures, polyesterstructures, or mixtures thereof
 6. The pulp of claim 5, wherein thepolyolefin is polypropylene or polyethylene.
 7. The pulp of claim 5,wherein the polyester is polyethylene terephthalate or polyethylenenaphthalate.
 8. The pulp of claim 1, wherein the polyarenazole is arigid rod polybenzazole or rigid rod polypyridazole polymer.
 9. The pulpof claim 8, wherein the polybenzazole is a polybenzobisoxazole.
 10. Thepulp of claim 8, wherein the polypyridazole is a polypyridobisimidazole.11. A filter material comprising the pulp of claim 1 and a binder.
 12. Afluid sealing material comprising the pulp of claim 1 and a binderselected from the group consisting of nitrile rubber, butadiene rubber,neoprene, styrene butadiene rubber, nitrile-butadiene rubber, andmixtures thereof.
 13. A thixotrope comprising the pulp of claim 1
 14. Aconcrete or masonry material reinforced by the pulp of claim 1
 15. Aprocess for making a fibrillated thermoplastic and polyarenazole pulpfor use as reinforcement material, comprising: (a) combining pulpingredients including: (1) thermoplastic fiber that is capable of beingfibrillated and having an average length of no more than 10 cm and being60 to 97 weight percent of the total solids in the ingredients; (2)rigid rod polyarenazole fiber having an average length of no more than10 cm and being 3 to 40 weight percent of the total solids in theingredients; and (3) water being 95 to 99 weight percent of the totalingredients; (b) mixing the ingredients to a substantially uniformslurry; (c) co-refining the slurry by simultaneously: (1) fibrillating,cutting and masticating the fibrillated thermoplastic fiber and thepolyarenazole fiber to irregularly shaped fibrillated fibrous structureswith stalks and fibrils; and (2) dispersing all solids such that therefined slurry is substantially uniform; and (d) removing water from therefined slurry, thereby producing a fibrillated thermoplastic andpolyarenazole pulp with the fibrillated thermoplastic and thepolyarenazole fibrous structures having an average maximum dimension ofno more than 5 mm, a length-weighted average length of no more than 1.3mm, and the fibrillated thermoplastic fibrils and/or stalks aresubstantially entangled with the polyarenazole fibrils and/or stalks.16. The process of claim 15, wherein the thermoplastic fiber has alinear density of no more than 10 dtex; and the polyarenazole fiber hasa linear density of no more than 2.5 dtex.
 17. The process of claim 15,wherein the thermoplastic fibrous structures are polyolefin structures,polyester structures, or mixtures thereof
 18. The process of claim 15,wherein the refining step comprises passing the mixed slurry through aseries of disc refiners.
 19. A process for making an fibrillatedthermoplastic and polyarenazole pulp for use as reinforcement andprocessing material, comprising: (a) combining ingredients includingwater and a first fiber from the group consisting of: (1) thermoplasticfiber that is capable of being fibrillated being 60 to 97 weight percentof the total solids in the pulp; and (2) rigid rod polyarenazole fiberbeing 3 to 40 weight percent of the total solids in the pulp; (b) mixingthe combined ingredients to a substantially uniform suspension; (c)refining the suspension in a disc refiner thereby cutting the fiber tohave an average length of no more than 10 cm, and fibrillating andmasticating at least some of the fiber to irregularly shaped fibrillatedfibrous structures; (d) combining ingredients including the refinedsuspension, the second fiber of the group of (a)(1 and 2) having anaverage length of no more than 10 cm, and water, if necessary, toincrease the water concentration to 95-99 weight percent of the totalingredients; (e) mixing the ingredients, if necessary, to form asubstantially uniform suspension; (d) co-refining the mixed suspensionby simultaneously: (1) fibrillating, cutting and masticating solids inthe suspension such that all or substantially all of the thermoplasticand polyarenazole fiber is converted to irregularly shaped fibrillatedthermoplastic and polyarenazole fibrous structures with stalks andfibrils; and (2) dispersing all solids such that the refined slurry issubstantially uniform; and (f) removing water from the refined slurry,thereby producing an thermoplastic and polyarenazole pulp with thefibrillated thermoplastic and the polyarenazole fibrous structureshaving an average maximum dimension of no more than 5 mm, alength-weighted average length of no more than 1.3 mm, and thethermoplastic fibrils and/or stalks are substantially entangled with thepolyarenazole fibrils and/or stalks.
 20. The process of claim 19,wherein the thermoplastic fibrous structures are polyolefin structures,polyester structures, or mixtures thereof